This invention relates to the integral flow measurement of centrifugal pumps, and more particularly to a flow measurement apparatus that utilizes differential pressure measurements at two separate locations within the volute section of the pump.
Centrifugal pumps are widely used in industry due to their compactness, simplicity, high efficiency, ease of maintenance and operation, and ability to deliver a stable flow of fluid. A typical centrifugal pump includes a housing with volute and discharge sections, both of which are in fluid communication with one another, and a rotating impeller. The volute section may comprise either single or multiple volutes. In general, the impeller imparts kinetic energy to the fluid, which moves circumferentially through the volute, past a volute lip and into the discharge. It is often desirable to monitor the flow of fluid through the pump to ensure that optimal process conditions are being met, and to do so in a way that is not susceptible to xe2x80x9cdownstreamxe2x80x9d flow obstructions that could induce erroneous readings. Since direct measurement of a fluid flow rate is a difficult undertaking, most flow measurements instead measure differences in static pressures at two different locations in a flow passage, then correlate that difference with a known flow constant, which is unique to the particular configuration of the flow measuring device. One of the advantages of using a flow constant to calculate flow rates is that the flow constant is not dependent on the aforementioned downstream conditions, although recommendations in terms of straight runs before and after the flow measurement device are usually made. Thus, an accurate measurement can be made irrespective of other constrictions, obstructions and the like found in the flowpath.
While flow measuring devices are routinely installed in more sophisticated, process-critical applications, their extra cost has traditionally not been warranted for many of the less expensive or more conventional pump applications. In recent years, however, the need to monitor even simple, inexpensive operations has marched in lock-step with end-user demands for consistent, repeatable, high-quality processes. Accordingly, the use of flow measurement sensors and ancillary support equipment for even conventional applications employing centrifugal pumps is in its ascendancy. However, the attachment of sensors and instrumentation to the pump can present significant cost and reliability burdens, in the form of installation and maintenance issues, especially when the sensor is exposed to harsh or heavily-travelled environments that increase the likelihood that they will be damaged or otherwise rendered inoperative.
It is therefore an object of the present invention to provide a centrifugal pump adapted for measuring fluid flow that overcomes the disadvantages of the prior art. According to a first aspect of the invention, a centrifugal pump includes a housing with an internal flowpath wall that defines volute and discharge sections, each section separated by a volute lip, an impeller, and pressure sensors integrally disposed in the housing wall. The impeller is disposed within the volute section, which in turn is defined by a circumferential path through which a fluid travels in response to impeller rotation. The discharge section is tangentially aligned and in fluid communication with the volute section such that fluid flowing through the volute section then passes through the discharge section. The volute lip section defines a bifurcation point between the volute and discharge sections. The sensors are embedded into the volute section of the housing wall such that they are exposed to a portion of the flowpath, thus placing them in fluid communication with liquid flowing therethrough such that they are responsive to changes in fluid pressure caused by variations in fluid flow.
The sensors may be circumferentially spaced apart in the volute section with one substantially adjacent the volute lip, with the other downstream such that the angle subtended between them is approximately 270xc2x0. The present inventors have discovered that the placement of the former sensor is such that, because the region it occupies captures very little flow (thus ensuring low dependence on flow rate), its use in conjunction with the latter sensor, placed in a downstream location in the volute section that, while dependent on flow, is relatively immune to further downstream conditions (such as those found closer to the exit plane of the discharge), thus resulting in a more accurate flow measuring system. A comparator device may be used to analyze the pressure measurements taken from each of the sensors, and a flow measurement output from the comparator is substantially linearly related to the difference in the pressure measurements taken from each of the sensors. As used in conjunction with the present disclosure, the term xe2x80x9csubstantiallyxe2x80x9d refers to an arrangement of elements or features that, while in theory would be expected to exhibit exact correspondence or behavior, may, in practice embody something slightly less than exact.
According to another aspect of the invention, a method of measuring fluid flow through a centrifugal pump is disclosed. The method includes the steps of configuring the pump to include a housing with an impeller disposed therein, a flowpath defined by a volute section, discharge section and volute lip section in fluid communication with one another, and a plurality of sensors circumferentially mounted to and spaced apart in the volute section; placing the pump in fluid communication with a fluid; operating the pump such that the fluid flows through at least a portion of the flowpath; taking measurements of the fluid at each location of the plurality of sensors; comparing the measurements taken at each of the locations with one another, thereby establishing a differential; inputting the differential into an algorithm configured to compare the differential to a flow constant; calculating a flow rate with the algorithm; and outputting the flow rate.
Optionally, the sensors used to take the measurements are pressure sensors, and the differentials established are pressure differentials. In addition, the flow rate can be output in human-intelligible or machine-readable format. A further step may involve transmitting the sensed signals from each of the plurality of sensors by a wireless transmitter to a signal comparator prior to comparing the measurements with one another. Also, a flow measurement output from the comparator is based on a linear relationship between the measurements of each of the plurality of sensors.
Other features and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims.